29-11 Radon-222 in Groundwater: Implications for Drinking Water Health Risk and Qualitative Assessment of Well Stagnation

Session: Undergraduate Research, Part II (Posters)

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This study investigates two aspects of ²²²Rn in groundwater: its role as a harmful gas dissolved in drinking water and its potential use as an indicator of groundwater stagnation in the well. We collected twenty 2-L groundwater samples from four municipal wells in Fulton, IL, with depths of 276, 1,260, 1,947, and 1,995 ft, to investigate the origin of radon and evaluate potential health effects associated with water consumption. The wells draw water from the shallow alluvial aquifer and deeper Cambrian bedrock aquifers. In addition, 6 2-L groundwater samples were collected from two private wells in Amboy, IL. These wells, with depths of 93 and 143 ft, draw water from a shallow Quaternary aquifer and an Ordovician shallow bedrock aquifer. Radon concentrations were measured using a RAD8. Well stagnation was evaluated by comparing the radon concentration of the first sample collected from a well (C₀) with the concentration after radon reached equilibrium (C_eq). ΔC = C_eq - C₀, was used as an indicator of the degree of stagnation. Preliminary results show that radon concentrations in the Fulton municipal wells ranged from 27.3 to 989 pCi/L in the first measurements and from 200.4 to 1,209 pCi/L in the second measurements. The ΔC values for the two private wells in Amboy were 461.6 and 26 pCi/L. Although the current data are preliminary, the results indicate variability in ²²²Rn concentrations among wells, likely reflecting differences in aquifer depth, lithology, and groundwater flow rates. Water from the two wells in Fulton exceeded the EPA’s 300 pCi/L drinking water limit. However, because these radon concentrations were measured prior to any filtration, treatment, or storage, they do not necessarily indicate a significant public health concern. For samples from Amboy, ΔC values suggest that radon concentration is sensitive to stagnation in wells due to its short half-life (t_1/2=3.82 days). However, stagnation cannot be interpreted independently of well construction and design. These preliminary findings suggest that dissolved radon may serve as a useful, but not universally applicable, indicator of well stagnation and potential health risks, while variations in Δ_C values can be used as a qualitative indicator of groundwater flow rates, with higher flow associated with lower ΔC.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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